By Mark Duff
BBC News, Milan
The proposal is widely seen as being anti-foreigner
A proposal to segregate trains on Milan's underground system has ignited the campaign for next month's European parliamentary elections in the city.
The idea came from Matteo Salvini, an MP from the regionalist and frequently anti-foreigner Northern League.
He suggested designating carriages exclusively for the use of registered Milanese residents and women.
The Northern League is part of Italian Prime Minister Silvio Berlusconi's centre-right government.
Mr Salvini argued that his idea was simply an extension of current arrangements reserving seats for the disabled and pregnant women.
Mr Salvini promoted his scheme as a way to fight crime and boost safety - a key campaign issue - and to combat the feeling that residents of Milan have become second class citizens in their own hometown.
Critics said it smacked of xenophobia.
The leader of Italy's biggest opposition party said it showed the centre-right government alliance was racist and recalled the struggle against segregation in the United States.
Many on the centre-right found also found the proposal offensive.
The president of the lower house of parliament, Gianfranco Fini - himself once an enthusiastic admirer of Benito Mussolini - said it offended human dignity and was contrary to the Italian constitution.
Mr Salvini's proposal is the latest in a long line of apparently anti-foreigner measures - many of them promoted by the Northern League.
In Treviso, near Venice, the local council restricted emergency help for people hit by the global economic crisis to Italian citizens and those resident in the country for more than five years.
In Foggia, in the far south, a local bus company introduced separate bus routes - one for immigrants, the other for residents.